In many communication transmission systems, there are multiple parallel transmissions bound together which can cause crosstalk between the lines. This results in a coupling between the achievable data rates of the lines within the binder, which means that increasing the transmit power, and thus the rate, of one link, may reduce the data rates of the other links. Transmissions in a cable binder are one example of such a communication transmission system. Crosstalk also occurs in wireless communication, in which adjacent or nearby channels may be subject to what is sometimes called “co-channel interference”. Many kinds of communication systems, with multiple communication lines or channels located in close proximity to one another, are subject to the phenomenon of crosstalk.
Typical solutions to this problem include physical separation of lines, mechanical shielding of lines from one another, and reduction in either the data rates or the communication quality or both, in the face of the effects of crosstalk. Another solution is called “Upstream Power Backoff”, in which a reference length of transmission and two parameters are used to calculate transmission powers assigned to each communication line at various times. As the number of communication lines increases, the scheduling complexities become such that typical optimization algorithms, including Upstream Power Backoff, simply cannot be used. Alternative solutions may then use other algorithms, such as iterative water filling, but none of these provide a perfect solution. Moreover, alternative solutions have disadvantages in that they cannot adjust power levels of multiple lines substantially in real-time, and they cannot switch between multiple pre-calculated configurations substantially in real-time.
Further, in the alternative solutions, a system may be planned as an optimal configuration for a particular optimization criterion. There are at least three such optimization criteria which may be implemented. Each optimization criterion is, at the time of its implementation, an alternative to the other two criteria, according to the alternative solutions. These three alternative implementation criteria are “absolute fairness”, which means maximizing the rate of the weakest link such that rate u=max mini(Ri), “relative fairness”, which means maximizing the overall system rate but subject to the condition that each remote terminal is communicating at a specific minimum, where u=max Σi(log Ri), or “system maximization”, which means maximizing the weighted sum of all data rates u=max Σi(wi·Ri).
The Digital Subscriber Line (DSL) technology, during all its history, attempted to increase the bit rate in the aim to deliver more broadband services to the customer. Unfortunately, copper loops deployed from the Central Office (CO) to customer premises equipment (CPE) are rather long and do not allow transmission of data with bit rates more than few Mb/s. Therefore, to increase the customer available bit rates, modern access networks use street cabinets, Multi Dwelling Unit (MDU)-cabinets, and similar arrangements: the cabinet is connected to the CO by a high-speed fiber communication line, e.g., gigabit passive optical network (GPON) and installed close to the customer premises. From these cabinets, high-speed DSL systems, such as Very-High-Bit-Rate DSL (VDSL), provide connection to the CPE. The currently deployed VDSL systems (ITU-T Recommendation G.993.2) have range of operation about 1 km, providing bit rates in the range of tens of Mb/s. To increase the bit rate of VDSL systems deployed from the cabinet, recent ITU-T Recommendation G.993.5 defined vectored transmission that allows increasing upstream and downstream bit rates up to 100 Mb/s.
Recent trends in the access communications market show that 100 Mb/s is still not sufficient for the close future, and bit rates up to 1 Gb/s are required. This could be only achieved if copper pairs connected the CPE to the fiber backbone are as short as 100 m-200 m. This requires installation of small street/MDU cabinets, called Distribution Points (DP) that intend to serve a very small number of potential users; the number of potential users shown by recent analysis internationally is 8-16, although some sources report higher required number of served users, like 24 or even 32. Therefore, DPs shall allow very flexible installation practices: they should be light and easily installed on a pole or house wall, or basement, without air-conditioning. These requirements bring substantial restrictions of the power consumption of a DP. Besides, DP (including housings and installed equipment) has to be very inexpensive, because with rather high probability, due to limited customer area, only a single subscriber may be connected to a particular installation for rather long time). Therefore, DP has to be equipped with a different type of transmission system than currently known DSL, that provides extremely low power consumption and inexpensive design, while provides very high bit rates (up to 1 Gb/s) and scalability to bigger number of users (if installed in protected environment, such as air-conditioned high-risers, for instance).
Two solutions were recently proposed for a DP:                a first approach that uses time division duplexing between upstream and downstream; and        a second approach that uses Synchronized Time Division Multiple Access (STDMA).        
The first approach requires higher power consumption and is more complex, but provides higher total bit rate (sum of all bit rate from the DP to the CPE) and what is called “sustainable bit rate”, which is an average bit rate guarantee for a service over a long period of time.
In the second approach, the sustainable bit rate is shared between users, and thus is lower than in case of the first approach and scales down as amount of users grows. Thus, in the case of many users the second approach may result in insufficient sustainable bit rate.
To cover all varieties of deployment scenarios and expected use cases, both approaches may be required. Therefore, a transmission method from a DP shall be capable to operate in a DP using either the first approach, the second approach or a combination of both.
The task of finding transceiver settings in a communication system that lead to a desired rate configuration, typically requires very complex optimization. The effort to find optimal parameters is often so serious and burdensome, that only inexact approximations of optimal settings are used. Further, as the number of lines in systems increase, the disadvantages of the alternative solutions become increasingly severe.